1. Field of the Invention
The present invention relates to a surgical implant for use in the replacement of a portion of a human toe joint and the method of use thereof.
2. Description of Related Art
Many people suffer from metatarsophalangeal joint (MPJ) complications, which present in association with hallux limitus, hallux rigidus, severe hallux valgus, joint deterioration and other bone and joint related conditions. Several types of prostheses have been developed to correct metatarsophalangeal joint complications. In particular, the prior art teaches different types of prostheses for total and partial joint replacement. In cases where a joint is in need of replacement, a total toe joint prosthesis is surgically implanted in association with resected bones at the joint. In general, a total joint prosthesis has two articulating members partially positioned in and adjacent to the respective bones associated with the joint in need of replacement. In cases where only one aspect of a joint is in need of replacement, a partial joint prosthesis with an articular surface is positioned partially within and adjacent to the resected bone at the joint in need of partial replacement. The articular surface of the partial joint prosthesis is designed to articulate with an articular bone surface of the non-resected bone in the joint.
Several prosthetic toe joints for total joint replacement are taught in the prior art. For example, an implantable toe joint is taught in U.S. Pat. No. 4,908,031. The implant has an articulating surface configured to articulate with another one-piece component with a mating concave bone surface or against a mating convex bone surface. The implant has two conically-shaped stems for insertion into corresponding intramedullary canals of the proximal phalanx and metatarsal bone of the foot. The implantable toe joint for replacing a human toe joint is made from flexible elastomeric, physiologically inert material. In addition, an implantable toe joint is taught in U.S. Pat. No. 4,642,122. The implantable joint includes a one-piece tack member with a cylindrical stem for implantation into the distal end of a metatarsal bone and a one-piece socket member with a pin, which is implantable into the proximal end of a phalanx. The pin has resilient, deflectable annular flanges, which sufficiently deflect upon insertion into the end of a phalanx to allow for self-locking in the phalanx. The implant is made from a combination of polyethylene material and metal alloy. The aforementioned prosthetic toe joints are advantageous in conditions indicating a total joint replacement, which is unnecessary in cases where only partial joint replacement is needed.
Several prosthetic implants for partial joint replacement are also taught in the prior art. For example, an anatomically correct great toe implant and surgical procedure for implanting the same is taught in U.S. Pat. No. 5,725,585. The great toe implant has a substantially reniform bearing surface, which provides a recess on the lower edge for receiving the flexor hallicus long tendon upon implantation. A stem is provided with the implant for positioning within the proximal phalanx during implantation. Retaining spikes are provided on the rear face of the implant to engage the proximal phalanx to prevent rotation of the implant after implantation. Additionally, a metatarsophalangeal resurfacing joint is taught in United States Patent Application Publication No. 2002/0072803. The joint has an ovoid-shaped base plate having a concave proximal bearing surface reciprocal to the shape of a head of a metatarsal, a flat rear surface and a gibbosity-shaped stem adapted for anatomical fit into an intramedullary canal of the proximal phalanx. Finally, a metatarsophalangeal resurfacing joint is taught in United States Patent Application Publication No. 2004/0230313. The joint comprises a base portion with a concave bearing surface to articulate with the distal articular surface of a metatarsal bone and a flat surface opposite the concave bearing surface to place against the resected surface of the proximal phalanx of the great toe. A stem extends from the flat surface of the base portion of the implant. The stem is generally frustoconical-shaped with a substantially oval wide end at the flat surface of the base portion, which tapers to a substantially circular end. The stem configurations of the aforementioned embodiments of partial toe joint implants present problems because none provides a mechanism for fixation to the interior surface of bone. A later effect of the problem, during and after surgery, is the ability of the implants to move in relation to the bones of the metatarsophalangeal joint.
Fixation of an implant is addressed with the biomechanical great toe implant taught in U.S. Pat. No. 5,326,366. The biomechanical great toe implant is used to resurface a damaged base of the proximal phalanx in a human great toe. The implant comprises a base, which is generally elliptical, with an anatomically-shaped proximal articular surface having a buildup on a lateral end. A generally planar distal surface is disposed on the base, opposite the articular surface of the base. An elongated stem with an array of fins extends from the planar distal surface of the base. The array of fins includes a cruciate-shaped cross section. The fins include a plurality of serrations along their sloping edges to anchor the stem within the cancellous portion of the proximal phalanx. The array of fins of the aforementioned implant presents a positioning problem when surgically implanting the implant within a phalanx as the serrations of the fins engage the cancellous portion of the phalanx. During positioning of the implant, the array of fins will engage the naturally porous interior portion of the phalanx without allowing for rotation, partial displacement and fixed positioning of the implant in a final position.
Accordingly, a present need exists for a partial toe implant and method therefor that provides a threaded mechanism for fixation of a stem of the implant within a medullary canal of a phalanx or other bone in the foot, and also provides an articular surface capable of anatomical fit with an articular surface of a bone.